Process of and apparatus for papermaking



March 26, 1963 G. F. UNDERHAY ETAL 25,358

PROCESS OF AND APPARATUS FOR PAPERMAKING Original Filed April 15, 1955 2Sheets-Sheet 1 INVEHTORS GEORGE FLAXMAH I/HDERHA; Jami NEIL FRANKLIN,and ARCHIBALD HOWARD WELLS By x A TTORHE Y5 March 26, 1963 G. F.UNDERHAY ETAL 25,353

PROCESS OF AND APPARATUS FOR PAPERMAKING 2 Sheets-Sheet 2 Original FiledApril 15, 1955 INVEHTORS:

GEORGE FLAXMAH UHDERHAY, 10H IIEIL FRANKLIN and ARCH/BALD HawARp- WELLSa; ATTORNEVS Re. 25,358 Reissued Mar. 26, 1963 25 358 PRWSESS F ANIiAPPARATUS FGR PAPERMAKIN G George Flaxman Underhay, Weybridge, England,John Neil Franklin, iiaie dUrfe, Montreal, Canada, and

Archibald Howard Wells, Gravesend, England, assignors to RowaterResearch and Development Company,

Limited, London, Engiand Original No. 2,919,495, dated lion. 5, 1960,ller. No.

561,615, Apr. 15, 1955. Appiication for reissue Sept.

27, W61, Ser. No. 142,452 0 Claims priority, application Great BritainApr, 15, 1954 Iii) Claims. (Ell. S t-23) Matter enclosed in heavybrackets E] appears in the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade by reissue.

This invention relates to a process of and apparatus for papermaking,more particularly to that stage of a papermaking process in which thewet web is dried.

In a typical papermaking machine the paper web, after leaving the wire,is passed, supported by felts, between press rolls with or withoutinternal suction boxes, so that the web is subjected to pressure andalso, in many cases, to vacuum to consolidate it and remove water. Afterleaving the press part of the machine the normal procedure is to passthe web, having a high moisture content and still containing some 60 to70% moisture, over a relatively large number of drying cylindersarranged in such a way that each side of the paper alternately comes incontact with the surface of the drying cylinders, the contact being madeas intimate as possible by means of felts which press the paper againstthe drying cylinders. This pressing action helps to promote the transferof heat to the paper and thus the rate of drying is increased.

Dryer felts are designed to have two opposing qualities, they aredesigned to be porous to allow for the passage of air and water vapourand they are also made absorptive to help carry away some of themoisture from the web. It is found, however, that felts, even under thebest possible operating conditions including the provision of adequatefelt dryers, hinder the ventilation of the web [and thus slow down therate of water removal].

The object of the invention is to provide a process of papermaking inwhich the paper web is dried more rapidly and under better control thanhas been possible heretofore.

This object is achieved, according to the invention, by a process ofpaperrnaking in which the paper web is dried by entrainment around aplurality of heated drying cylinders wherein the web is maintained inclose but non-adhesive contact with [the] a cylinder [surfaces] surfaceby the force of air acting on the exposed surface of the web, the airbeing caused to flow over the exposed surfaceand thus helping to removemoisture expelled from the web by the action of the heated [cylinders]cylinder.

The main advantages of the process according to the invention are:

a. Due to the increased rate of drying the overall size of the dryingsection of a papermaking machine employing the above process may be madesmaller than those used at present.

b. As a consequence of the paper being exposed on one side to theatmosphere or to the air flow all or substantially all the time it isbeing heated, the removal of moisture across the Width of the sheet willbe much more readily controllable enabling the finished sheet to have amoisture content substantially uniform across the full width even beforethe paper is dampened, should this be necessary for any reason.

0. The paper, passing over and with one face of the web in contact withonly a drying cylinder, and with the other face of the web exposed toair flow, can more easily be allowed to shrink naturally during thedrying process and therefore it will possess stretching properties.which will reduce the risk of rupture under tensile stress.

In the [preferred] process the [main] general direction of air flow [isin} may be [a direction] generally opposite to [and parallel with] thedirection of movement of the web.

The invention also provides a drying section for a papermaking machinewhich comprises a [plurality of] heated drying [cylinders] arrangementaround which the web to be dried will be entrained, a hood or hoodsarranged circumferentially with respect to [some at least of the] one ormore drying cylinders, means for urging the web into close butnon-adhesive contact with [each] the hooded cylinder or cylinders as theweb is about to enter under a hood or h ods, and means for forcing airthrough the hood or hoods to flow over the exposed surface of the weband maintain it in close non-adhesive contact with the hooded cylinderor cylinders so as to remove the moisture expelled from the web.

In certain instances the shrinkage of the paper during drying provides atension in the web which has the effect of assisting in holding the webin contact with the cylinder or cylinders. This effect [is] appc'ars tobe most pronounced in some cases when the web has dried to the pointwhere its moisture content is around 25 to 35 percent.

The force exerted on the exposed surface of the web is only suflicientto maintain the Web in contact with the cylinder 0r cylinders and is notso great as to cause the web to stick to the cylinder or cylinders as isusual in the maunfacture of glazed papers.

Preferably the hood or hoods is or are divided into a plurality ofsections parallel to the direction of movement of the web and eachsection is provided with a plurality of circumferentially spaced airducts having orifices for directing air into the weband connectedthrough a control valve to a suitable air supply.

The means for initially urging the web into contact With [each] acylinder may comprise either a nip roll or a felt acting in conjunctionwith the cylinder, or a suction device adapted to create a partialvacuum in the wedge-shaped space where the web meets the cylinder.

An embodiment of the invention will now be described by way of examplewith reference to the accompanying drawings wherein:

FIGURE 1 shows diagrammatically an elevation of part of the dryingsection of a papermaking machine in accordance with the invention,partly in section on the line -II in FIGURE 3,

FIGURE 1A is a fragmentary elevation showning some of the partsillustrated in FIGURE 1, but including a modified arrangement forinsuring that the paper web, when it comes to a drying cylinder, willget closely into contact with the cylinder,

FIGURE 2 shows in section on enlarger scale a modified form of a portionof the machine shown in FIG- URE 1, and

FIGURE 3 shows, partly in section, an end view of part of the machinetaken in the direction of the arrow III in FIGURE 1, certain parts beingomitted for clarity.

The drying section of a papermaking machine compris ing severalrotatable heated cylinders 1a, 1b, 1c five only being shown in FIGURE 1,of a larger diameter than are normally used. A convenient diameter maybe,

for example, between eight and twelve feet. The cylinders are arrangedat two levels, the center of a cylinder at one level being midwaybetween the centers of the adjacent two cylinders at the other level asis clearly shown in FIGURE 1. The paper web A is entrained about andpasses ver the first two cylinders 1a, 1b transversely to the cylinderaxes with supporting felt 17 passes, otherwise unsupported, and aboutthe remaining cylinders without the use of felts and the portion of thecircumference of each of the remaining cylinders 1c, 1d, 1e with whichthe web is in contact is surrounded by a [hood 2.] h od means 2circumferentially embracing at least in part the portion of the cylinderover which the web is entrained. Each hood 2 is divided into sections,that is, zones or chambers 3 as shown in FIGURE 3 by partitions 4running in the direction of the paper web and being spaced apart in thedirection of the cylinder axis; and the number of sections may be asgreat as twelve or so, depending on the width of the machine, so thatthe air conditions applying over diiferent portions of the width of thepaper may be independently controlled [.1 within the separated chambers3 deployed across the cylinder in the direction of the cylinder axis andrespectively embracing correspondingly deployed parts of the web.

An air inlet flow means, as shown a supply manifold [5] means 5 commonto the several chambers 3 is provided adjacent each hood 2 and axiallyparallel therewith and from each manifold 5 distributor pipes 6 arecarried over the hood in a direction substantially parallel to thedirection of motion of the web A on the cylinder. A control valve 16 isprovided for each distributor pipe 6' [.1 for individually anddifferentially controlling the flow of air in the several chambers 3 incontact with the cylinderentrained web. There is a distributor pipe 6corresponding to each section 3 disposed substantially centrally withrespect to the section, and from each pipe 6 further connecting pipes 7connect the distributor pipe to a number of ducts within the hood 2,each duct having an air inlet opening facing toward thecylinder-entrained web, as shown an orifice 9 arranged to direct airwithin the duct, and fed from the manifold 5 through the distributor andconnecting pipes 6, 7, onto the outer surface of the web A as it passesover the surface of the cylinder. Air outlet openings 9a facing awayfrom the cylinder-entrained web are provided by the spaces betweenadjacent ducts 8, the sets of inlet and outlet openings in each chamberbeing deployed circumferentially of the cylinder in spaced relation toone another, and the air outlet openings of one set being interspersedbetween the air inlet openings of the other set.

Adjacent the main edge of each hood 2, at which the paper web A enters,an exhaust pipe i.e. duct 10 connects each section 3 to an air outlet flw means, as shown an exhaust manifold duct 18' [J common to the severalchambers 3. The exhausted air may be allowed to pass out to theatmosphere or it may be re-circulated to the supply manifold throughsuitable drying and compressing means for re-use. Air which has beenremoved from the hoods and recirculated through drying means for re-usewill be in a more dry state when re-used than when removed from thehoods.

The partitions 4 of each hood 2 extend as close to the paper web A asnormal engineering practice will permit, but it is by no means essentialthat leakage from one section 3 to another should be avoided [.1provided the air inlet flow means 5 and the air outlet flow means 18.communicate separately with the chambers 3 independently of flow of airfrom chamber-to-chamber.

Seals at the main edges of the hood 2 parallel to the axis of thecylinder may be produced by providing these edges with a flexible doctorblade or rubbing strip 11 and positioning this to bear on a roll 12which itself is bearing on the paper on the drying cylinder. One of therolls 12 may constitute a nip roll to bring the paper web A enteringupon the drying cylinder into close contact with the cylinder.

Instead of using a nip roll to ensure that the paper, when it comes to adrying cylinder, will get closely into contact with the cylinder theremay be employed means indicated at 19 in FIGURE 1A for sucking air outof the wedge-shaped space 13 between the paper and the drying cylinder.

In a modification, a short length of felt 14 may be provided as shown inFIGURE 2 to bring the web onto the cylinder surface, the hood beingsealed by a flexible doctor blade 11 as before.

The side edges of each hood are sealed by resilient members 15 hearingon the surface of the cylinder thereunder.

The air which is forced through the hoods is at a pressure aboveatmospheric pressure, a suitable value being of the order of about 0.5lb. per square inch, or possibly less.

An important feature of the invention is that it will allow the amountof air used for removing the water from the web to be closely controlledby means of the valves 16 across the width of the Web A. The amount ofair admitted to each section of the hood and the temperature of thesupply is controllable enabling, for example, more air to be sent to themiddle of the machine, where paper often tends to be more difficult todry, and less air to either or both the edges where the paper may drymore quickly.

It will be appreciated that the process according to the invention maybe applied to existing papermaking machines and that although dryingcylinders of larger diameter than normal are preferred, normal sizedcylinders may be used.

We claim:

{1. A drying section for a papermaking machine comprising a plurality ofheated drying cylinders around which the paper web to be dried will beentrained, a plurality of hoods arranged circumferentially with respectto at least some of the cylinders, means for urging the web into closebut non-adhesive contact with each of said hooded cylinders as the Webis about to enter under the hood, a plurality of partitions spaced apartalong the length of each hooded cylinder within the associated hood anddividing the hood into a plurality of sections, a plurality of separateair supply pipes associated with each of said sections, and a pluralityof separate ducts within each section, each of said ducts beingconnected to a different one of said air supply pipes and having adischarge orifice in proximal relationship to the associated hoodedcylinder and each of said ducts providing an air charnber enlarged inrelation to the associated air supply pipe and discharge orifice] [2. Adrying section for a papermaking machine comprising a plurality ofheated drying cylinders around which the paper web to be dried will beentrained, a plurality of hoods arranged circumferentially with respectto at least some of the cylinders, means for urging the web into closebut non-adhesive contact with each of said hooded cylinders as the webis about to enter under the hood, a plurality of partitions spaced apartalong the length of each hooded cylinder within the associated hood anddividing the hood into a plurality of sections, a plurality of separateair supply pipes associated with each of said sections, a plurality ofseparate ducts within each section, each of said ducts being connectedto a different one of said air supply pipes and having a dischargeorifice in proximal relation to the associated hooded cylinder and eachof said ducts providing an air chamber enlarged in relation to theassociated air supply pipe and discharge orifice, a plurality ofdistributor pipes respectively connected to the air supply pipesassociated with said sections, and separate valves for individuallycontrolling the flow of air into said distributor pipes] [3. A dryingsection for a papermaking machine comprising a plurality of heateddrying cylinders around which the paper Web to be dried Will beentrained, a plurality of hoods arranged circumferentially with respectto at least some of the cylinders, means for urging the web into closebut non-adhesive contact with each of said hooded cylinders as the Webis about to enter under the hood, a plurality of partitions spaced apartalong the length of each hooded cylinder within the associated hood anddividing the hood into a plurality of sections, a plurality of separateair supply pipes associated With each of said sections, a plurality ofseparate ducts Within each section, each of said ducts being connectedto a different one of said air supply pipes and having a dischargeorifice in proximal relationship to the associated hooded cylinder andeach of said ducts providing an air chamber enlarged in relation to theassociated air supply pipe and discharge orifice, sealing means alongthe edges of the hoods adjacent the surfaces of the hooded cylinders forpreventing egress of air from said hoods, and exhaust manifold means forreceiving air to be discharged from Within said hoodsj 4. A dryingsection for a paperrnaking machine comprising a plurality of heateddrying cylinder around which the paper Web to be dried Will beentrained, a plurality of hoods arranged circumferentially with respectto at least some of the cylinders, a plurality of partitions spacedapart along the length of each hooded cylinder within the associatedhood and dividing the hood into a plurality of sections, a plurality ofseparate air supply pipes associated with each of said sections, and aplurality of separate ducts within each section, each of said ductsbeing connected to a different one of said air supply pipes and having adischarge orifice in proximal relationship to the associated hoodedcylinder and each of said ducts providing an air chamber enlarged inrela tion to the associated air supply pipe and discharge orifice.

5. A drying section for a papermaking machine comprising a plurality ofheated drying cylinders around which the paper Web to be dried Will beentrained, a plu rality of hoods arranged circumferentially with respectto at least some of the cylinders, a plurality of partitions spacedapart along the length of each hooded cylinder Within the associatedhood and dividing the hood into a plurality of sections, a plurality ofseparate air supply pipes associated With each of said sections, aplurality of separate ducts Within each section, each of said ductsbeing connected to a different one of said air supply pipes and having adischarge orifice in proximal relation to the associated hooded cylinderand each of said ducts providing an air chamber enlarged in relation tothe associated air supply pipe and discharge orifice, a plurality ofdistributor pipes respectively connected to the air supply pipesassociated With said sections, and separate valves for individuallycontrolling the flow of air into said distributor pipes.

[6. A drying section for a papermaking machine comprising a plurality ofheated drying cylinders around which the paper Web to be dried Will beentrained, a plurality of hoods arranged circumferentially with respectto at least some of the cylinders, a plurality of partitions spacedapart along the length of each hooded cylinder within the associatedhood and dividing the hood into a plurality of sections, a plurality ofseparate air supply pipes associated with each of said sections, aplurality of separate ducts Within each section, each of said ductsbeing connected to a dififerent one of said air supply pipes and havinga discharge orifice in proximal relationship to the associated hoodedcylinder and each of said ducts providing an air chamber enlarged inrelation to the associated air supply pipe and discharge orifice,sealing means along the edges of the hoods adjacent the surfaces of thehooded cylinders for preventing egress of air from said hoods, andexhaust manifold means for receiving air to be discharged from Withinsaid hoods] 7. In apparatus for drying a paper web in a papermakingmachine, a cylinder around a substantial portion of which a paper web tobe dried is to be entrained and passed thereover transversely t thecylinder axis; hoo-ll means circumfercmially embracing, at least inpart,

the portion of said cylinder over which the web is to be entrained andenclosing a plurality of air flow zones deployed across the cylinder inthe irection of the cylinder axis and respectively embracingcorrespondingly cleployecl ports of the cylinder-entrained web; airinlet flow means communicating with said zones; air outlet duct meanscommunicating with said zones individually at locations spaced axiull'yof said cylinder whereby to remove air from the respective zonesindividually without substuntial air flow in contact with the web fromzone-t0- zoize axially of said cylinder; and means for delivering air tosaid air inlet flow means to flow upon the portion of the web entrainedaround and in contact with said cylinder under pressure sufficient tomaintain said web portion in non-adhesive contact with said cylinder andfor individually and dificrcntia'lly controlling air flowing within saidzones in contact with the cylinder-entrained web as the latter passesover said cylinder.

8. In apparatus for drying a paper web in a papermokihg machine, acylinder around a substantial portion of which a paper web to be driedis to be entrained and passed thereover transversely to the cylinderaxis; hood means circumfercniially embracing, at least in port, theportion of said cylinder over which the web is to be entrained andenclosing a plurality of air flow zones deployed across the cylinder inthe direction of the cylindcr axis; a plurality of air inlet openingscommunicating with each of said air flow zones, being deployedcircumferentially of said cylinder and facing toward saidcylinder-entrained web for elivering air against the web where thelatter is in Contact with said cylinder; a plu raliiy of air outletopenings communicating with each of mill air flow zones, being deployedcircum-fcrcntially of said cylinder, facing away from saidcylinder-entrained web and being interspersed between said air inletopenlugs; and means for controlling the air drying of said webdifierentiolly across the web in said air flow zones.

9. In apparatus for drying a paper web in a papermuking machine, acylinder around a substantial portion 09 which a paper web to be driedis to be entrained and passed thereover transversely to the cylinderaxis; hood means circumferentially embracing, at least in part, theportion of said cylinder over which the web is to be entrained,- aplurality of partitions within said hood extending transversely of saidcylinder axis, being spaced apart in the direction of extent of thecylinder axis and providing a plurality of separated chambers deployedacross the cylinder in the direction of the cylinder axis andrespectively embracing correspondingly deployed parts of thecylinder-entrained web; air inlet flow means communicating separatelywith said chambers independcnlly of flow of air from any of saidchambers to others thereof; air outlet duct means communicating withsaid chambers individually at locations spaced axially of said cylinderwhereby to remove air from the respective chombers individually withoutsubstantial air flow in Contact with the web from chambcr-to-chahzbcraxially of said cylinder; means for delivering air to said air inletflow means for elivery to said chambers and upon the portion of the webentrained around and in contact with said cylinder under pressuresufiicicnt to maintain said web portion in non-adhesive contact withsaid cylinder,- and means for indivi ually and diflcrentiallycontrolling the flow of air through said chambers in contact with theweb.

10. In apparatus for drying a paper web in a papermalcing machine, acylinder around a substantial portion of which a paper web to be driedis to be entrained and passed thereovcr transversely to the cylinderaxis; hood moons circumfcrentially embracing, at least in part, theportion of said cylinder over which the web is to be entrained; aplurality of partitions within said hood extending transversely of saidcylinder axis, being spaced apart in the direction of extent of thecylinder axis and providing a plurality of separated chambers deployedacross the cylinder in the direction of the cylinder axis andrespectively embracing correspondingly deployed parts of thecylinder-entrained web; air inlet flow means communicating separatelywith said chambers independently of flow of air from any of saidchambers to others thereof; air outlet duct means communicating withsaid chambers individually at locations spaced axially of said cylinderwhereby to remove aid from the respective chambers individually withoutsubstantial air flow in contact with the web from chamber-to-chamberaxially of said cylinder; and means for individually and difierentiallycontrolling air flowing within said chambers in contact with thecylinder-entrained web as the latter passes over said cylinder.

11. In apparatus for drying a paper web in a papermaking machine, acylinder around a substantial portion of which a paper web to be driedis to be entrained and passed thereover transversely to the cylinderaxis; hood means circumferentially embracing, at least in part, theportion of said cylinder ver which the web is to be entrained; aplurality of partitions within said hood extending transversely of saidcylinder axis, being spaced apart in the direction of extent of thecylinder axis and providing a plurality of separated chambers deployedacross the cylinder in the direction of the cylinder axis andrespectively embracing correspondingly deployed parts of thecylinder-entrained web; air inlet flow means communicating separatelywith said chambers independ ently of flow of air from any of saidchambers to others thereof; air outlet duct means c mmunicating withsaid chambers individually at locations spaced axially of said cylin erwhereby to remove air from the respective cham bers individually withoutsubstantial air flow in contact with the web from chamber-to-chamberaxially of said cylinder; and separate valves connected respectivelybetween individual chambers and said air inlet flow means forindividually controlling the flow of air within each chamber in contactwith the cylinder-entrained web.

12. In apparatus for drying a paper web in a papermaking machine, acylinder around a substantial por tion of which a paper web to be driedis to be entrained and passed thereover transversely to the cylinderaxis; hood means circumferentially embracing, at least in part, theportion of said cylinder over which the web is to be entrained; aplurality of partitions with said hood extending transversely of saidcylinder axis, being spaced apart in the direction of extent of thecylinder axis and providing a plurality of separated chambers deployedacross the cylinder in the direction of the cylinder axis andrespectively embracing correspondingly deployed parts of thecylinder-entrained web; a set of air inlet openings within each of saidchambers deployed circumferentially of said cylinder in spaced relationto one another and facing toward the cylinder-entrained web fordelivering air thereagainst in circumferentially separated streamsflowing inwardly toward said cylinder-entrained web; a set of air outletopenings within each of said chambers deployed circumferentially of saidcylinder in spaced relation to one another, facing away from thecylinder-entrained web and being interspersed between the air inletopenings in the associated chamber for removing air from thecylinder-entrained web outwardly with respect to said cylinder; meansfor delivering air to the air inlet openings of the several chambers;duct means for exhausting air from the respective sets of air outletopenings of the several chambers individually at locations spacedaxially of said cylinder whereby to remove air from the respectivechambers individually without substantial air flow in contact with theweb from chamber-to-chamber axially of said cylinder; and means forcontrolling the flow of air in the respective chambers.

13. In apparatus for drying a paper web in a papermaking machine, acylinder around a substantial portion of which a paper web to be driedis to be entrained and passed thereover transversely to the cylinderaxis; hood means circumferentially embracing, at least in part, theportion of said cylinder over which the web is to be entrained; aplurality of partitions within said hood extending transversely of saidcylinder axis, being spaced apart in the direction of extent of thecylinder axis and providing a plurality of separated chambers deployedacross the cylinder in the direction of the cylinder axis andrespectively embracing correspondingly deployed parts of the cyliner-entrained web; a set of air inlet openings within each of saidchambers deployed circumferentially of said cylinder in spaced relationto one another and facing toward the cylinder-entrained web fordelivering air thereagainst in circumferentially separated streamsflowing inwar ly toward said cylinder entrained web; a set of air outletopenings within each of said chambers deployed circumferentially of saidcylinder in spaced relati n to one another, facing away from thecylinder-entrained web and being interspersed between the air inletopenings in the associated chamber for removing air from thecylinder-entrained web outwardly with respect to said cylinder; commonmeans for de livering air to the air inlet openings of the severalchambers; common duct means for exhausting air from the air outletopenings of the several chambers individually at locations spacedaxially of said cylinder whereby to remove air from the respectivechambers individually without substantial air flow in contact with theweb from chamber-to-chamber axially of said cylinder; and separatevalves connected respectively between one of said common means and oneof the sets of openings within each of said chambers for individuallycontrolling the flow of air in contact with difierent portions of saidweb passing respectively through said across-the-cylinder deployedchambers.

14. In a method of drying a paper web in a papermaking machine, passingthe web over a drying cylinder; delivering air upon the surface of theportion of the web in contact with the cylinder in separate zonesdeployed axially of the cylinder so as to remove moisture from the weband to apply sufiicient pressure to the said surface of the web tomaintain the web in close non-adhesive contact with the cylinder;removing the moisture laden air from said zones individually after saidair has passed over said surface of said web whereby the air is removedfrom contact with the web without substantial air flow over the web fromzone-to-zone, re-delivering upon said web air which has been removedtherefrom but which is in a more dry state than when removed, andindividually and ifierentially contr lling the flow of air in said zonesin contact with the web axially of the cylinder.

References Cited in the file of this patent or the original patentUNITED STATES PATENTS 1,129,156 Woodsome Feb. 23, 1915 1,438,211 BaetzDec. 12, 1922 1,470,953 Bassler Oct. 16, 1923 1,724,645 De Long Aug. 13,1929 1,738,641 Cowan Dec. 10, 1929 1,830,287 Ohlin Nov. 3, 19311,995,999 Oxian Mar. 26, 1935 2,022,593 Fuykers Nov. 26, 1935 2,166,379Skagcrberg July 18, 1939 2,218,282 Downs Oct. 15, 1940 2,304,818 GrupeDec. 15, 1942 2,366,484 Bradner J an. 2, 1945 2,526,012 Feldmeier Oct.17, 1950 2,622,343 Mctcalfe Dec. 23, 1952 FOREIGN PATENTS 280,776 GreatBritain Nov. 24, 1927

